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Tides
are caused by the gravitational pull of the sun but primarily
the moon, since it is much closer to the earth. It takes the
moon 29 1/2 days to orbit the earth, or 12° each day. The
earth rotates once in 24 hours. From one moonrise to the next,
the earth makes one rotation plus the additional 12° which
takes approximately 24 hours 50 and 1/2 minutes. This pulling
effect on the earth causes a bulge of the ocean nearest the
moon and a bulge on the opposite side of the earth. These two
bulges are the position of high tide. The
earth rotates but the bulges stay lined up with the moon.
As your location rotates, you have high
tide, low tide, high tide, low tide and the cycle repeats. Each
high tide will be about 25 min. later than the last. Tides
can vary from the affects of strong winds, changes in amospheric
pressure, the position of the sun. These factors can cause
the tide to be early for some periods- late for others, but
the tide always returns to the regular cycle. A tide clock
gives a general indication of tidal activity but is not recommended
where precise marine navigation is required.
Setting a tide clock on a full moon gives the most accurate results. You need
only reset it on the full moon once. To set, insert battery as indicated on
the movement. Turn the set knob (it’s easier using a pencil in the hole
in the little wheel) until the hand indicates the stage of the tide at your
favorite location. It is easiest to set the tide clock at the exact time of
the predicted high, but should it be, for example, two hours before or after,
you may set the clock to indicate that reading.
Use a long life battery for best results;
remove battery if clock is not going to be in use for long
periods of time to prevent corrosion. Tide clocks are only
to be used where there are diurnal tides. Other tidal areas
require frequent resetting.
For tide tables to set your tide clock, click
here. |